The disposal of residual gases generated in industrial processes by means of combustion is well known. In the electronics and semiconductor industries, for example, a waste gas typically containing low concentrations of gaseous toxic substances represented by arsine (AsH3), phosphine (PH3), diborane (B2H6), silane (SiH4), etc. is formed in the steps for manufacturing semi-conductors. Since this waste gas is highly toxic, complete elimination of such toxic substances contained in the waste gas is necessary prior to exhausting of the waste gas into the atmosphere.
Another source of residual, and often toxic, gases arises from the refilling of cylinders employed for providing such source gases to various industries. Spent cylinders previously used in an electronics processing facility containing residual gases, for example, are returned to a transfill facility. Before such cylinders are refilled, they are generally purged and/or evacuated to remove all contaminants, generating a cylinder purge gas often having a high concentration of toxic gas. These cylinder purge gases must also be treated prior to discharge to the atmosphere.
Various methods are known for effectively eliminating such toxic gases and these methods include combustion. The combustion methods contemplate oxidative decomposition of the toxic substances in the residual, waste gas under combustion conditions whereby the gaseous toxic substances are oxidatively converted into less reactive, often innocuous, reaction products including solid oxides.
A major problem in the combustion of flammable, and often toxic gases, which generate solid phase oxidation products is one of nozzle plugging and particle build-up in the combustion chamber. Recirculation of the solid phase products in the combustion process often leads to significant deposition of finely divided particles on the burner nozzles thus interfering with combustion. Build-up of the particles can lead to aggregation and potential for incomplete combustion of the residual gases. Intermediate products of incomplete combustion can burn in a downstream part of the process that can sometimes lead to safety issues (e.g., burning holes in filter bags). Complete plugging of the burner nozzles can lead to a pressure increase in the system creating safety issues.
The following references illustrate various combustion processes for the disposal of combustible and often toxic feed gases that form solid phase oxidation products many of which are commonly used in the electronics industry:
U.S. Pat. No. 5,957,678 discloses a combustion type detoxifying apparatus for the removal of raw gases such as silane comprised of a combustion chamber, a precombustion chamber located at the top of the combustion chamber and a multi-wall burner attached to the precombustion chamber. The multi-wall pipe type burner has: (1) a raw gas nozzle for injecting the feed gas, which is located at the center, (2) a lift gas nozzle for injecting a lift gas, which is arranged to surround the raw gas nozzle, (3) a feed gas combustion-assisting gas nozzle for injecting a gas for assisting combustion of combustible components in the feed gas (i.e., a first oxidant), which is arranged to surround the lift gas nozzle, (4) a fuel gas combustion-assisting gas nozzle for injecting a gas for assisting combustion of a fuel gas (i.e., a second oxidant), which is arranged to surround the residual gas combustion-assisting gas nozzle, and (5) a fuel gas nozzle for injecting the fuel gas, which is arranged to surround the fuel gas combustion-assisting gas nozzle.
The combustion chamber has a double wall structure containing a cylindrical outer barrel coupled with a fluid nozzle, a porous inner barrel having a constitution such that powders may be prevented from depositing on the inner surface of the inner barrel. If powdery solid oxides are formed during combustion treatment of the raw waste gas, such powders are prevented from being deposited on the inner surface of the inner barrel and interfering with the combustion treatment by passing a pressure fluid through the nozzle in the outer barrel. Thus, the combustion treatment can be carried out in a stable state over an extended period.
U.S. Pat. No. 4,801,437 discloses a process for combusting poisonous and solid forming gases such as silane, dichlorosilane, germane, etc., wherein combustible exhaust gases and an inert gas, primary and secondary air are downwardly fed through a coaxial, fourfold pipe burner provided with an innermost combustible exhaust gas path, and inert gas path, a primary air path and an outermost secondary air path to form downward flames for combustion. Downward flow is alleged to reduce the amount of deposition of fine dust such as silicon dioxide resulting from combustion on the burner nozzle.
U.S. Pat. No. 5,123,836 discloses the combustion treatment of a toxic gas which forms microparticles on combustion. The toxic feed gas is combusted and the combustion gas brought into contact with an aqueous film flowing downward on the inner wall of a furnace from the upper end to the lower end. The water captures the microparticles formed on combustion.